Nonlinearity mitigation of intensity modulation and coherent detection systems.

Area of Science:

• Optical Communications
• Signal Processing

Background:

• Coherent optical systems are too expensive for metro networks.
• Intensity modulation with coherent detection offers a cost-effective alternative but is limited by nonlinearity.

Purpose of the Study:

• Investigate nonlinearity in high-speed intensity modulation and coherent detection systems.
• Propose advanced digital signal processing (DSP) for nonlinearity mitigation.

Main Methods:

• Developed a 2x1 MIMO complex Volterra FFE filter.
• Implemented a novel post-FFE noise cancellation filter.
• Utilized a maximum likelihood sequence estimator.
• System uses an integrated laser and electro-absorption modulator.

Main Results:

• Proposed nonlinear DSP achieved over 8 dB and 4 dB OSNR sensitivity improvement compared to linear FFE for 7% and 20% FEC overheads, respectively.
• Demonstrated a record 18 dB OSNR sensitivity at a 3.8x10^-3 BER threshold.
• Achieved 56 Gb/s data rates.

Conclusions:

• Advanced nonlinear DSP offers significant performance gains for intensity modulation and coherent detection systems.
• This approach provides a viable, cost-effective solution for metro and short-reach optical networks.
• The proposed DSP does not require carrier and phase recovery, simplifying receiver design.